Traction system for electrically powered vehicles

ABSTRACT

Fixed frequency, fixed duration pulse streams are used to control power switches for one or more electrical motors of electrically powered vehicles or hybrid vehicles having one or more electric motors. The advantages of a pulse system are increased power efficiency and system simplicity over analog systems. The capability of system calibration with a single pulse allows the system to be used under any conditions, and real time adaptation to changes in conditions. Such system and methods provide much improved acceleration over other electrical systems, by making the best use of the coefficient of starting or static friction. The systems and methods provide a non slip traction control system, and the use of an off state in the pulse stream is superior to the use of braking systems for the same purpose, which waste power and cause mechanical wear. In addition, related computer program products are described.

BACKGROUND

Electric motors can exhibit a high torque output from very low revolutions per minute (RPM). Internal combustion engines, have very low torque at low RPMs, their torque increasing with increasing RPM to peak at a maximum, usually above 1000 RPM. However, the high torque of electrical motors cannot be utilised efficiently since the high torque will cause the driven wheel of the car to skid or slide. The maximum possible acceleration of a car on wheels is limited by the laws of physics, specifically, the coefficient of friction.

The coefficient of friction between two surfaces has two distinct parts: the coefficient of sliding friction (also known as just coefficient of friction), and the coefficient of starting friction (also known as the coefficient of static friction). For ease of discussion, the coefficient of sliding friction can be designated as C_(slide) and the coefficient of starting friction as C_(start). The coefficient of sliding friction, C_(slide), defines the force required to keep an object sliding on a surface, specifically, F=(W)X(C_(slide)), where F is the force required to keep an object of weight W sliding on a surface which has a C_(slide) (coefficient of sliding friction) for the two materials which compose the object and the surface on which it is sliding. C_(slide) is dependent on the two materials and is independent of moderate speeds, although it usually decreases slightly above 30 to 40 feet per second. C_(slide) is less than 1.0 and is always lower than C_(start) for the same object on the same surface, i.e. for any given material on any given surface, C_(start)>C_(slide).

The coefficient of starting friction, C_(start), refers to the force required to cause an object at rest to begin sliding on a surface. The required force to start an object sliding is: F=(C_(start))X(W). C_(start) is greater than C_(slide), so once the object begins to slide, it requires less force keep the object sliding.

The acceleration imparted on a car is limited by the coefficient of friction, i.e., A=F/M, where: A=acceleration, F=the force applied to the car, and M=the mass of the car. Since the force for acceleration F is limited by the coefficient of friction, thus the acceleration is limited by C_(slide) and C_(start).

A sliding wheel can impart a forward force on the car equal to the force due to the coefficient of sliding friction, i.e., F=(W)X(C_(slide)), where F is the imparted force of acceleration, Cslide is the coefficient of sliding friction between the tire of the driven wheel and the road, (which varies considerable with the type of road surface, and conditions such as temperature, wetness, etc.), and W is the combined total weight of the tire onto the road surface.

If the wheel is not skidding, then the forward force of acceleration can be as high as F=(W)X(C_(start)). Since Cstart>Cslide, the possible acceleration is greater as long as the wheel does not skid or slide. Thus the traction of a tire on the road is significantly higher when the surface of the tire is at rest relative to the surface of the road, as opposed to when the surface of the tire is sliding or skidding relative to the surface of the road. This does not mean that the tire is not moving; in fact, the tire may be travelling at a great speed, but if the tire is rotating at the correct rate, the bottom surface of the tire will match the speed at which the surface of the road meets the tire; that is, the tire is rolling on the road. All that matters is that the two surfaces of the tire and the road are momentarily at rest with respect to each other, where the two surfaces meet. The traction in that case is thus limited by Cstart.

If the two surfaces of the tire and road are moving relative to one another, then the traction is limited by C_(slide). Since C_(start)>C_(slide), the traction in the first case greatly exceeds the second case. It is exactly this principle which is the basis for many anti-lock braking systems (“ABS”), which lessen the braking action when wheel skid is detected, allowing the tire to freewheel, and to re-establish zero relative speed and thus provide conditions for C_(start).

Previous traction techniques for vehicles having internal combustion engines or electric motors have been limited in ability to apply torque to drive wheels under various road conditions and with optimal energy efficiency.

SUMMARY

It is to be understood that both the foregoing summary of the present disclosure and the following detailed description are exemplary and explanatory and are not intended to limit the scope of the present disclosure. Moreover, with regard to terminology used herein, a reference to an element in the singular is not intended to mean “one and only one” unless specifically stated, but rather “one or more.” The term “some” refers to one or more. Underlined and/or italicized headings and subheadings are used for convenience only, do not limit the present disclosure, and are not referred to in connection with the interpretation of the description of the present disclosure.

Aspects and embodiments of the of the present disclosure address problems previously for previous traction techniques for electrically powered vehicles and are directed to fixed frequency, fixed duration pulse streams used to control the power switch(es) for the electrical motor(s) of an electric car (or hybrid powered car). The advantages of such pulse-based techniques include increased power efficiency and system simplicity over analog systems. The capability of calibration with a single pulse allows such techniques to be used under any conditions, and also for real time adaptation to changes in road surface conditions and acceleration needs. These fixed frequency, fixed duration pulses techniques can provide much improved acceleration over other electrical systems, by making the best use of the coefficient of starting (or static) friction. Pulses of Fixed Frequency Fixed Duration (FFFD) can be superior to pulse width modulation (PWM) and variable frequency pulses in providing very accurate power pulses for precision control. FFFD pulses supply nearly exact packets of power with each pulse, thus allowing an exact measure of power to the wheels in nearly identical packets, and thereby making full use of the force to the wheel before it breaks from the Cstart condition. The systems and methods of the present disclosure can provide for a non-slip traction control. The use of an off state in the pulse stream is very superior to the use of ABS braking systems for the same purpose, which waste power and cause mechanical wear, since convention ABS makes use of braking forces rather than acceleration forces.

One skilled in the art will appreciate that embodiments and/or portions of embodiments of the present disclosure can be implemented in/with computer-readable storage media (e.g., hardware, software, firmware, or any combinations of such), and can be distributed over one or more networks. Steps described herein, including processing functions to derive, learn, or calculate formula and/or mathematical models utilized and/or produced by the embodiments of the present disclosure, can be processed by one or more suitable processors, e.g., central processing units (“CPUs), implementing suitable code/instructions in any suitable language (machine dependent on machine independent).

Additionally, embodiments of the present disclosure can be embodied in signals and/or carriers, e.g., control signals sent over a communications channel. Furthermore, software embodying methods, processes, and/or algorithms of the present disclosure can be implemented in or carried by electrical signals, e.g., for downloading from the Internet. While aspects of the present disclosure are described herein in connection with certain embodiments, it should be noted that variations can be made by one with skill in the applicable arts within the spirit of the present disclosure.

Other features of embodiments of the present disclosure will be apparent from the description, the drawings, and the claims herein.

BRIEF DESCRIPTION OF THE DRAWINGS

Aspects of the disclosure may be more fully understood from the following description when read together with the accompanying drawings, which are to be regarded as illustrative in nature, and not as limiting. The drawings are not necessarily to scale, emphasis instead being placed on the principles of the disclosure. In the drawings:

FIG. 1 depicts diagrammatic cross section views of a tire and wheel in different states of loading and slipping relative to an underlying surface;

FIG. 2 depicts four graphs of wheel and tire dynamics for different loading and spin conditions in accordance with the embodiments of the present disclosure: (A) Force v. Time, (B) Wheel RPM v. Time, (C) Applied Torque, and (D) Force v. Time;

FIG. 3 depicts two sets of plots (A)-(B) illustrating how embodiments of the present disclosure can provide the maximum impulse force in acceleration by synchronizing the torque ON pulses to four wheels of a vehicle;

FIG. 4 depicts an exemplary algorithm or flow chart for establishing a fixed-frequency fixed-duration pulse stream for controlling power to an electrical engine supplying power to one or more wheels;

FIG. 5 depicts an exemplary algorithm or flow chart for supplying power with fixed-frequency fixed-duration pulse streams for four-wheel drive vehicles; and

FIG. 6 depicts a box diagram of an exemplary system, in accordance with embodiments of the present disclosure.

While certain embodiments are depicted in the drawings, one skilled in the art will appreciate that the embodiments depicted are illustrative and that variations of those shown, as well as other embodiments described herein, may be envisioned and practiced within the scope of the present disclosure. Accordingly, the drawings and detailed description are to be regarded as illustrative in nature and not as restrictive.

DETAILED DESCRIPTION

In the following detailed description, numerous specific details are set forth to provide a full understanding of aspects and embodiments of the present disclosure. It will be apparent, however, to one ordinarily skilled in the art that aspects and embodiments of the present disclosure may be practiced without some of these specific details. In other instances, well-known structures and techniques have not been shown in detail to for ease in comprehension.

Embodiments of the present disclosure accommodate and take into account all of the variables in road/tire conditions, by taking measurement of the first pulse with wheel slip, and then providing fixed frequency, fixed duration pulse streams to control the power switch(es) for the electrical motor(s) of an electric car (or hybrid powered car). The resulting wheel rotation is continuously monitored, and upon any discrepancy from the expected pattern, a single pulse measurement is used to refresh the FFFD pulse stream with new timing values. Thus changes in road surface, tire loading from turning, or any other variations, are quickly and automatically compensated.

FIG. 1 depicts diagrammatic cross section views of a tire and wheel in different states of loading and slipping relative to an underlying surface while FIG. 2 depicts four graphs of wheel and tire dynamics for different loading and spin conditions in accordance with the embodiments of the present disclosure: (A) Force v. Time, (B) Wheel RPM v. Time, (C) Applied Torque, and (D) Force v. Time.

FIG. 1 shows a wheel 110 and tire 112, at rest relative to a road, 120, and under different degrees of stress and loading (A)-(C). Since the tire is not moving relative to the road (note: these conditions apply even when the car is in motion, the wheels in freewheel mode) there is no forward stress on the tire, as shown by tire stress condition (or, strain) 130. As a large acceleration torque 140 is applied to the wheel, this causes the tire and related structure to be stressed, as shown by stress condition 150. By first approximation, the structure reacts as a spring, which means that the relationship between distortion and force is primarily linear in mathematical terms.

FIG. 2 depicts four graphs of wheel and tire dynamics for different loading and spin conditions in accordance with the embodiments of the present disclosure: (A) Force v. Time, (B) Wheel RPM v. Time, (C) Applied Torque, and (D) Force v. Time. FIG. 2 illustrates the dynamics involved for a situation where a wheel and tire contacting an underlying surface such as pavement experience a condition where the available torque to turn this wheel is sufficiently high to overcome C_(start). The force of acceleration on the car caused by this wheel is shown in FIG. 2A. The force 220, is shown increasing from zero (at time 225), linearly, as the torque is applied to the wheel; this would continue approximately linearly, except that the car would start to accelerate, as shown by the wheel rotation 242 and 244. This relieves the stress on the tire somewhat, and the curve 220 starts to flatten out. However, since the available torque from the electrical motor is greater than that allowed by C_(start), 250, when inevitably curve 220 reaches the value 250, the wheel will start to slide, or skid, at time 230, with the tire rotation increasing very quickly, 246, instead of increasing as expected 248.

The skid or slide means that the friction between the tire and the road is determined by C_(slide), and as seen by the curve 235, the acceleration force falls to level 255 fairly quickly. So long as the wheel is skidding (or spinning), the maximum traction possible is level 255, as indicated by 215. However, by turning OFF the torque as soon as wheel spin is detected, the wheel recovers to its non stressed state just as quickly, 247. The end of recovery 247 is used to mark time 240, which defines the end of time period 295, the recovery time. It is important to note that the values for C_(start), C_(slide), and thus the shapes of the curves, and thus the times 230 and 240, all vary with changing conditions such as wetness, temperatures of the road and tire, type of road surface, etc. The values of C_(start), C_(slide), can also change with weight loading of the car on that tire, air resistance on the car and tire, and even if the wheel has lateral (turning, or side-loading) forces at the same time. What is also important is that under all these variations, C_(start) is always higher that C_(slide), so that the general principles hold true.

As noted previously, embodiments of the present disclosure can accommodate and take into account all of the variables in road/tire conditions, by taking measurement of the first pulse with wheel slip, i.e., monitoring and recording the time duration 292 and 295. Pulses to be used in subsequent acceleration of this wheel are the repeated, for a given or specified time domain (or period of time), by using the time (pulse widths) 295 and 292 to generate the pulse train shown by maximum torque applied ON for a period of time 260, and the torque OFF for a period 265, repeating, 267, as long as the driver keeps indicating a desired increase in speed or until an intervening condition or command occurs, e.g., wheel slip or braking occurs.

As a result, an acceleration force is supplied to the wheel and tire, as shown by curve 290. Note that the average of this acceleration force is at level 275, which is lower than the absolute maximum level 280, but higher than the spinning wheel level 270.

With reference again to FIG. 1, it may be noted that the unstressed state, 130, does not depend on the car to be stopped, only that the tire is at rest relative to the road; i.e. the car can be in motion at any speed. Thus as long as the torque OFF period 265 of FIG. 2 is sufficiently long to allow the curve 290 to fall momentarily below the Cslide level 270, and establish zero relative speed between tire and road surfaces, then the initial condition 130 of FIG. 1 is re-established. It should be noted that the recovery time need not be exactly the period T2, 295. It is not necessary for the torque force to fall to zero; only that it fall below Cslide, 255, which re-establishes the zero slip condition. T2, 295 can be used in the system software for recovery, or a slightly higher or lower time period allotted for recovery, in order to customize performance “feel”.

By using the first pulse to determine the period lengths of T1 292 and T2 295, all variations in the ambient conditions are accompanied. Once T1 292 and T2 295 are established, the pulse train 267 is of Fixed Frequency and Fixed Duration. The system is responsive in real time. The wheel rotation can monitored at desired times or continuously, (e.g., as shown in FIG. 4 at 480 and FIG. 5 at 575) and if the wheel slip is longer than the recovery time 295, or if it is absent completely, then the system reinitializes in the very next pulse. This can be done since only one pulse is required to reset the pulse timing for changing road conditions or change in system performance (lower available engine torque, shift in weight distribution, etc.) as the car increases speed.

While the average acceleration 275 shown in FIG. 2D is less than the theoretical maximum of 280, the approach of using pulsed power according to the present disclosure has several practical advantages relative to previous approaches. For example, pulses systems according to the present disclosure can automatically compensate for varying C_(start) and C_(slide) values by measuring the first pulse upon a required acceleration; analog systems must somehow determine these values accurately and quickly. Electronic analog power control systems are less efficient than pulse systems in power efficiency, a critical factor when electric cars are limited by battery capacity. Additionally, analog power control systems are more complex in design and manufacture.

As well, pulsed systems and methods according to the present disclosure can be self correcting. When the car is moving at a high speed and the electrical motor is operating at higher RPMs and the torque capability is no longer greater than Cstart imposes, then the curve 220 flattens considerably more, and never crosses the Cstart level 250. Thus there is no end to the initial pulse, and the maximum available power from the electrical motor is kept in the ON state for the duration. Note that this maximum acceleration system is imposed only when the car's computer detects a requirement for fast acceleration i.e. heavy throttle setting; however, the same system can be activated by the car's computer to insure that there is minimal wheel slippage, thus providing an active, pulsed traction control system.

For certain situations maximum acceleration force is required. For example, a situation in which a four-wheel drive (4WD) wheel drive vehicle must be moved out of a mired condition, it is greatly desirable to have the maximum forward force applied to the vehicle. For a 4WD vehicle, it is preferable that all four wheels accelerate in unison; not just nearly in unison, but exactly in unison. If, for example, four persons are attempting to push a car out of a snowbank, then all four persons ideally would apply their shove synchronously, so as to maximize the impulse on the stuck vehicle; if one person is out of synch with the others, then his or her impulse is not added to the peak impulse of the other three persons, and the maximum peak forward force is not realized.

FIG. 3 depicts two sets of plots (A)-(B) illustrating how embodiments of the present disclosure can provide the maximum impulse force in acceleration by synchronizing the torque ON pulses to four wheels of a vehicle.

FIG. 3 shows how a method embodiment 300 of the present disclosure can be used to provide the maximum impulse force in acceleration by synchronizing the torque ON pulses to all four wheels. 310, 315, 320, and 325 represent the torque On/Off states for four wheels which are not time synchronized. The resulting total torque for the four wheels is represented by 330. 330 shows that the maximum total force is, in this example, 3. In contrast, 340, 345, 350, and 355 show four similar wheels with similar torque duty cycles, which are time synchronized. The total force 360 reaches a value of 4 on each pulse cycle. By utilizing the same Fixed Frequency/Fixed Duration pulses at each of the four wheels synchronously, the maximum forward force possible is imparted to the car.

FIG. 4 depicts an exemplary algorithm 400 or flow chart for establishing a fixed-frequency fixed-duration pulse stream for controlling power to an electrical engine supplying power to one or more wheels.

FIG. 4 shows a typical subroutine logic to establish the fixed frequency/fixed duration pulse stream which controls the power to the electrical engine. When the requirement for additional acceleration is received from the car's on board computer, the system initializes, 410. The data for the wheel rotational rate noted, and the system initiates with the calibrating ON pulse, 420. The timer is started to measure the pulse length initiated by 420. The wheel rotation is monitored for slippage, 430, and if none is detected, the pulse continues in the ON mode; the requirement for additional acceleration is continuously monitored as well, by 440, “not complete”. This loop 430, 440, can continue until wheel slippage or the requirement for acceleration is completed or no longer needed.

If there is a wheel slippage detected, then the ON pulse can be terminated, 445, and the length of the pulse (T2, FIG. 2, 292) is stored and the Off state sent to the engine power control. The wheel slippage is monitored for recovery to non-slip condition, and the elapsed recovery time (FIG. 2, 295) is stored, 450. The system then generates the string of fixed frequency/fixed duration pulse in loop 460, 470, 480, until the acceleration requirement if fulfilled as per the car's computer, or an unusual slippage condition (too long, or completely absent) is detected, at which time the system reinitializes, 490. When there is no wheel slippage, this system maintains the constant On power state when maximum acceleration is required, and when the conditions of the wheel rotation change, the system reinitializes and recalibrates within a single pulse. The onboard computer of the vehicle can initiate this system at any time without requiring acceleration, just to keep the wheels in the non-slip condition, i.e., an active traction control, non skid system, FIG. 4 input to 410, 440, under car's CPU control.

FIG. 5 depicts an exemplary algorithm 500 or flow chart for supplying power with fixed-frequency fixed-duration pulse streams for four-wheel drive vehicles, such as shown to be required in FIG. 3. While not show, a variation for 2 wheel drive vehicles can be derived, and is not discussed. Also, all principles from FIG. 4 are assumed for FIG. 5, but for simplicity, not shown. FIG. 5, 510 shows the car's CPU requesting maximum acceleration. As previously mentioned, the car's CPU can simply poke this system in a non-acceleration way, to change from a maximum acceleration system to a traction control system. Since any one or more of the wheels may be on a very poor traction state, eg wet ice, where Cstart is very low, a minimum pulse duration period is established, in the order of 15 milliseconds, 520. This minimum pulse can be adjusted in software to accommodate various car configurations or “performance feel”. After the minimum pulse period, if any of the wheels are slipping, 530, they are not used to determine the pulse ON length, 540. The CPU processor executes its instructions in microseconds, whereas the wheel rotation and slippage detection is in the millisecond range, thus the digital processing of the data and software are inconsequential to the mechanics of the system.

Subsequently, 550 and 560 determine the fixed frequency, fixed duration pulse lengths for the wheels with significant traction, 570 uses this pulse stream to drive all four wheels simultaneously; even if one or more wheel may be slipping, once the car move ever so slightly, the slipping wheels may gain traction, It is important to maintain synchronicity to achieve maximum forward impulse force. Loop 580, 585, and 575 continue the system logic until the acceleration requirement is removed (i.e., the car moves or the driver throttles back).

It will be understood that algorithm 500 can be stored in any suitable computer readable medium, e.g., flash memory, ROM, EEPROM, RAM, hard discs, etc., and may be coded in any suitable language (machine dependent or machine independent). Moreover, such an algorithm may be a functional component of suitable software and can be stored in firmware and/or hardware. Additionally, such an algorithm or software can be run or performed by any suitable processor.

FIG. 6 depicts a box diagram of an exemplary system 600, in accordance with embodiments of the present disclosure. The power can be electrical, and can either AC or DC, 610. This power can be switchable ON and OFF, 620, and this on/off state should be controllable by an outside signal, 670. The switched power can run an electrical motor 630, which in turn drives the cars wheel(s), 640. The rotation of the wheels should be monitored by servo or other methods, with sufficient resolution for our purposes, 650. The system CPU, 660, can receive commands from the car's CPU, 680 for throttle setting and traction control mode. The CPU can utilize these inputs 680, 650, to generate the pulse control signals, 670 which in turn can switch the Motor power on and off, 620. Variations of this configuration are possible, including the incorporation of hybrid power (gasoline assisted) systems, which will be automatically compensated by the first pulse calibration method of this present disclosure under all conditions. Moreover, one electric motor can supply power to an axle, with or without a differential mechanism. For exemplary embodiments, a separate electric motor is provided to drive each wheel of the vehicle.

FIG. 6 also shows additional respective power switches 620 and electric motors 630 for additional wheels (2)-(4) of a representative vehicles. For such applications, the related sensing system would detect the wheel motion of those additional wheels and the controller or additional controllers would control the torque and power supplied to the additional wheel by supplying a fixed duration fixed frequency control signal as described previously.

While some specific descriptions of aspects and embodiments of the present disclosure have been provided, there may be many other ways to implement various aspects and embodiments of the present disclosure. Various functions and elements described herein may be partitioned differently from those shown without departing from the spirit and scope of the present disclosure. Various modifications to these embodiments will be readily apparent to those skilled in the art, and generic principles defined herein may be applied to other embodiments. Thus, many changes and modifications may be made, by one having ordinary skill in the art, without departing from the spirit and scope of the present disclosure and claimed embodiments. 

1. A system for controlling power applied to one or more drive wheels of a vehicle, the system comprising: an electric motor configured and arranged to supply power for driving a wheel; a wheel configured and arranged to receive power from the electric motor; a controller configured and arranged to (i) receive acceleration commands and wheel slip information for the wheel as inputs, and (ii) produce as an output a control signal for the electric motor driving the wheel, wherein the control signal includes a timing cycle with a series of pulses of fixed duration and fixed frequency within the timing cycle to cause current to flow to the electric motor during an ON component of the timing cycle; and a current switch connected to the electric motor including an input to receive the control signal to place the switch in one of an ON state and an OFF according to the timing cycle.
 2. The system of claim 1, wherein the controller is configured and arranged to adjust the timing cycle of the pulses of fixed frequency and fixed duration.
 3. The system of claim 2, wherein the controller is configured and arranged to adjust the timing cycle based on a sensed coefficient of friction of the driving wheel.
 4. The system of claim 1, wherein the controller is configured and arranged to provide real-time adjustment of the power supplied to the wheel, wherein changing traction conditions can be accommodated.
 5. The system of claim 1, wherein the system is configured and arranged for automatic measurement, storage, and use of the pulse length for the ON pulse.
 6. The system of claim 1, wherein the system is configured and arranged for automatic measurement, storage, and use of the pulse length for the OFF pulse.
 7. The system of claim 1, wherein the wheel slip information comprises a coefficient of starting friction and/or coefficient of sliding friction.
 8. The system of claim 1, further comprising a second electric motor, a second wheel, and a second current switch, wherein the controller is configured and arranged to (i) receive acceleration commands and wheel slip information for the second wheel as inputs, and (ii) produce as an output a control signal for the second electric motor driving the second wheel, wherein the control signal includes a timing cycle with a series of pulses of fixed duration and fixed frequency within the timing cycle to cause current to flow to the second electric motor during an ON component of the timing cycle, and wherein the second current switch is connected to the second electric motor and includes an input to receive the control signal to place the second current switch in one of an ON state and an OFF according to the timing cycle.
 9. The system of claim 1, further comprising a third electric motor, a third wheel, and a third current switch, wherein the controller is configured and arranged to (i) receive acceleration commands and wheel slip information for the third wheel as inputs, and (ii) produce as an output a control signal for the third electric motor driving the third wheel, wherein the control signal includes a timing cycle with a series of pulses of fixed duration and fixed frequency within the timing cycle to cause current to flow to the third electric motor during an ON component of the timing cycle, and wherein the third current switch is connected to the third electric motor and includes an input to receive the control signal to place the third current switch in one of an ON state and an OFF according to the timing cycle.
 10. The system of claim 1, further comprising a fourth electric motor and a fourth wheel, wherein the controller is configured and arranged to (i) receive acceleration commands and wheel slip information for the fourth wheel as inputs, and (ii) produce as an output a control signal for the fourth electric motor driving the fourth wheel, wherein the control signal includes a timing cycle with a series of pulses of fixed duration and fixed frequency within the timing cycle to cause current to flow to the fourth electric motor during an ON component of the timing cycle, and wherein the fourth current switch is connected to the fourth electric motor and includes an input to receive the control signal to place the fourth current switch in one of an ON state and an OFF according to the timing cycle.
 11. The system of claim 1, wherein the duration of each pulse of the current switch control signal is equal to the period of time between pulses in the timing cycle.
 12. The system of claim 1, wherein the duration of each pulse of the control signal is less than or equal to the period of time between pulses in the timing cycle.
 13. The system of claim 1, wherein the number of pulses in a timing cycle varies from zero to a maximum number corresponding to an acceleration level of the electric motor from zero to a maximum acceleration.
 14. The system of claim 1, further comprising a processing system to generate the current switch control signal supplied to the current switch and to time the start and end of each pulse within the timing cycle.
 15. The system of claim 1, wherein the length of the timing cycle is constant and the acceleration of the vehicle is varied by changing the number of pulses from one timing cycle to another timing cycle.
 16. The system of claim 10, wherein the controller is configured and arranged to provide synchronization of pulses provided to the four electric motors for synchronized four-wheel drive operation.
 17. The system of claim 8, wherein the controller is configured and arranged to detect which wheels have a minimum acceptable traction for inclusion in a synchronized power pulse provided to the wheels.
 18. The system of claim 17, wherein the detection of the minimum acceptable traction is based on a minimum time before a slide starts to occur.
 19. The system of claim 18, wherein the minimum time is about 15 milliseconds.
 20. The system of claim 10, wherein the controller is configured and arranged to detect which wheels have a minimum acceptable traction for inclusion in a synchronized power pulse provided to the wheels.
 21. The system of claim 20, wherein the detection of the minimum acceptable traction is based on a minimum time before a slide starts to occur.
 22. The system of claim 21, wherein the minimum time is about 15 milliseconds.
 23. A method for controlling the power applied to one or more electric motors coupled to one or more wheels of an electrically powered vehicle, the method comprising: providing a timing cycle; determining a desired acceleration rate for a vehicle powered by one or more electrically driven wheels; generating a control signal including a series of pulses of fixed duration and fixed frequency within the timing cycle corresponding to the desired acceleration rate; and supplying control signal to an input of a current switch connected to one or more electric motors, each connected to a respective one of the one or more wheels, to place the switch in one of an ON state during each pulse and an OFF state after each pulse to cause current to flow to the respective electric motor connected to each electrically driven wheel during the ON state and cause the respective electric motor to supply a desired power to each electrically driven wheel over the timing cycle.
 24. The method of claim 23, wherein the one or more electrically driven wheels comprises two wheels.
 25. The method of claim 23, wherein the one or more electrically driven wheels comprises four wheels.
 26. The method of claim 23, wherein providing a timing cycle includes establishing a timing cycle of a constant length and the power applied to each wheel is varied by changing the number of generated pulses from one timing cycle to another timing cycle.
 27. The method of claim 24 wherein the duration of each pulse of the control signal is equal to the period of time between pulses in the timing cycle.
 28. The method of claim 24 wherein the duration of each pulse of the control signal is less than or equal to the period of time between pulses in the timing cycle.
 29. The method of claim 24 wherein the number of pulses in a timing cycle varies from zero to a maximum number corresponding to a power level of an electric motor from zero to a maximum power level.
 30. The method of claim 23, further comprising adjusting the timing cycle of the pulses of fixed frequency and fixed duration.
 31. The method of claim 30, wherein adjusting the timing cycle is based on a sensed coefficient of friction of the driving wheel.
 32. The method of claim 31, wherein adjusting the timing cycle comprises real-time adjustment, wherein changing traction conditions can be accommodated.
 33. The method of claim 23, further comprising automatic measurement, storage, and use of the pulse length for the ON pulse.
 34. The method of claim 23, further comprising automatic measurement, storage, and use of the pulse length for the ON pulse.
 35. The method of claim 23, further comprising sensing wheel slip information, wherein the wheel slip information comprises a coefficient of starting friction and/or coefficient of sliding friction.
 36. The method of claim 23, wherein supplying control signal comprises providing synchronization of pulses provided to two or more electric motors for synchronized two-wheel drive or four-wheel drive operation.
 37. The method of claim 23, further comprising detecting which wheels have a minimum acceptable traction for inclusion in a synchronized power pulse provided to the wheels.
 38. The method of claim 37, wherein detecting the minimum acceptable traction is based on a minimum time before a slide starts to occur.
 39. The method of claim 38, wherein the minimum time is about 15 milliseconds.
 40. A computer program product residing on a computer-readable storage medium having a plurality of instructions stored thereon, which when executed by a processing system, cause the processing system to: provide a timing cycle; determine a desired acceleration rate for a vehicle powered by one or more electrically driven wheels; generate a control signal including a series of pulses of fixed duration and fixed frequency within the timing cycle corresponding to the desired acceleration rate; and supply a control signal to an input of a current switch connected to one or more electric motors, each connected to a respective one of the one or more wheels, to place the switch in one of an ON state during each pulse and an OFF state after each pulse to cause current to flow to the respective electric motor connected to each electrically driven wheel during the ON state and cause the respective electric motor to supply a desired power to each electrically driven wheel over the timing cycle.
 41. The computer program product of claim 40, wherein the computer-readable storage medium comprises flash memory.
 42. The computer program product of claim 40, wherein the computer-readable storage medium comprises ROM memory.
 43. The computer program product of claim 40, wherein the one or more electrically driven wheels comprises two wheels.
 44. The computer program product of claim 40, wherein the one or more electrically driven wheels comprises four wheels.
 45. The computer program product of claim 40, wherein providing a timing cycle includes establishing a timing cycle of a constant length and the power applied to each wheel is varied by changing the number of generated pulses from one timing cycle to another timing cycle.
 46. The computer program product of claim 40, wherein the duration of each pulse of the control signal is equal to the period of time between pulses in the timing cycle.
 47. The computer program product of claim 40, wherein the duration of each pulse of the control signal is less than or equal to the period of time between pulses in the timing cycle.
 48. The computer program product of claim 40, wherein the number of pulses in a timing cycle varies from zero to a maximum number corresponding to a power level of an electric motor from zero to a maximum power level.
 49. The computer program product of claim 40, further comprising instruction to adjust the timing cycle of the pulses of fixed frequency and fixed duration.
 50. The computer program product of claim 40, further comprising instruction to adjust the timing cycle based on a sensed coefficient of friction of the driving wheel.
 51. The computer program product of claim 40, further comprising instruction to adjust the timing cycle for real-time adjustment, wherein changing traction conditions can be accommodated.
 52. The computer program product of claim 40, further comprising instruction for automatic measurement, storage, and use of the pulse length for the ON pulse.
 53. The computer program product of claim 40, further comprising instruction for automatic measurement, storage, and use of the pulse length for the OFF pulse.
 54. The computer program product of claim 40, wherein the wheel slip information comprises a coefficient of starting friction and/or coefficient of sliding friction.
 55. The computer program product of claim 40, further comprising instruction for providing synchronization of pulses provided to two or more electric motors for synchronized two-wheel drive or four-wheel drive operation.
 56. The computer program product of claim 40, further comprising instruction for detecting which wheels have a minimum acceptable traction for inclusion in a synchronized power pulse provided to the wheels.
 57. The computer program product of claim 56, wherein detecting the minimum acceptable traction is based on a minimum time before a slide starts to occur.
 59. The computer program product of claim 57, wherein the minimum time is about 15 milliseconds. 